|Author: ||R.K. Arora|
|Keywords: ||Phytophthora infestans, loss, races, tolerance to metalaxyl|
The north-western plains of India, due to their low aphid population in autumn, have emerged as prime seed producing areas in India and cater to a large demand of quality seed all over the country.
Data recorded on appearance and build up of late blight for the past 27 years (1980-2006) revealed that the disease, which used to occur in mild to moderate form and epiphytotic only once in 4 to 5 years, is more recently steadily assuming epiphytotic proportions almost every alternate year.
It appeared in epiphytotic form in 3 out of 4 years from 2003 to 2006. A comprehensive survey on loss in yield caused by late blight carried out during the 2006- 07 crop season revealed an average loss of 22% in productivity resulting in a net loss of around 0.16 million tons of potato in the state of Punjab alone.
The increase in disease severity in recent years could be due to a change in the pathogen population.
An analysis of 91 isolates of Phytophthora infestans collected from different areas in the Punjab region during 2006 revealed the presence of 11-gene complex races in 58.5% of the isolates and a tolerance to metalaxyl beyond 200 ppm in 22.0% of the isolates, underlining a drastic change from the simpler races and zero tolerance to metalaxyl recorded in the earlier years.
Moreover, the disease now appears comparatively earlier and within a higher temperature range of 14.0-27.5°C than before when its usual appearance occurred after the third week of November in a temperature range of 10-25°C. During 2006, the disease appeared on November 8 which was the earliest recorded date in the past 27 years.
The increasing severity of late blight, the shift in the pathogen population and the increasing tolerance to metalaxyl suggests the need for the development of an appropriate disease management strategy.
Download Adobe Acrobat Reader (free software to read PDF files)
URL www.actahort.org Hosted by KU Leuven